The present invention relates generally to solar energy receiving devices, and more particularly, to a receiving device and heat engine for generating mechanical energy to operate machinery or produce electricity.
Using solar energy to power various devices is useful in reducing the dependency of the country on fossil fuels. Solar power systems include photovoltaics that generate electricity directly from sunlight and solar power systems that use conventional power cycles and machinery such as Brayton or Rankine. The latter are currently competitive with photovoltaics on a cost per kilowatt basis.
One drawback in the implementation of such devices commercially is the expense associated therewith. The expense, for example, is due to the high costs of materials, and various other complexities involved with such systems. One expensive portion of such systems is a primary heat exchanger. Such a heat exchanger is relatively expensive and increases the cost of the system.
It would therefore be desirable to reduce the cost of a solar power system by simplifying the design and increasing the economy of manufacture and thus the subsequent utilization of such devices.
The present invention provides an improved solar receiver design that reduces the cost of such devices.
In one aspect of the invention, a solar receiver includes a heat pipe having a working fluid therein. The heat pipe has a first condenser portion disposed at a first end and a second condenser portion disposed at a second end. The heat pipe further includes an evaporator portion disposed between the first end and the second end. An air manifold is coupled to the first end. The air manifold has an air inlet and an air outlet. A liquid manifold is coupled to the second end. The liquid manifold has a liquid inlet and a liquid outlet. The evaporator portion of the heat pipe receives the solar energy which is disposed of at the gas and the liquid cooled ends of the heat pipe.
In a further aspect of the invention, a method for operating a solar receiver includes heating a working fluid in a heat pipe to form heated working fluid, circulating the heated working fluid within the heat pipe, heating air outside the heat pipe to form heated air. The method further includes converting the heated air into mechanical energy, heating liquid outside the heat pipe at a second end to form a heated liquid, and storing thermal energy from the heated liquid. The processes of heating the air and heating of the liquid may be adjusted to occur simultaneously in any proportion by adjusting the flowrates of the gas and the liquid.
One advantage of the invention is that a primary heat exchanger typically used in such systems is eliminated. Further, the use of a minimum inventory liquid loop to supply energy to phase change or other types of thermal energy storage units reduced the overall cost of the system.
Another advantage of the invention is that it may be operated using a thermal storage device to supply energy to the receiver upon the passage of clouds or for pre and post-daylight operation.
Another advantage of the invention is that heat stored in the thermal storage device may be used to activate or start the heat pipe without the use of solar energy incident on the evaporator section of the pipe. This can result in a significant reduction of thermal strain on the heat pipe, thereby significantly increasing heat pipe fatigue life.
Another advantage of the invention is that the Brayton turbomachinery can be preferentially located at the top of the tower where it can be close coupled to the receiver. This results in minimizing the pressure drop between the compressor and expansion stages of the turbine, thus minimizing the impact of gas heater pressure drop on turbine performance.
Other aspects and advantages of the present invention will become apparent upon the following detailed description and appended claims, and upon reference to the accompanying drawings.